"The entire Biden family is saddened beyond words", the vice-president said.

In a statement, President Barack Obama said: "Michelle [Obama] and I are grieving tonight."

"Beau was a good, big-hearted, devoutly Catholic and deeply faithful man, who made a difference in the lives of all he touched - and he lives on in their hearts."

In a Twitter post, former President Bill Clinton wrote: "Hillary & I mourn the loss of Beau Biden - so full of life, love, honor, and service - and we pray for the strength of his wonderful family."

'Spirit will live on'

Beau Biden was diagnosed with brain cancer in August 2013 and underwent treatment that was initially successful. However, the cancer recurred earlier this year.

Announcing the death in a statement, the vice-president said: "It is with broken hearts that Hallie, Hunter, Ashley, Jill and I announce the passing of our husband, brother and son, Beau, after he battled brain cancer with the same integrity, courage and strength he demonstrated every day of his life."

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Vice-President Biden visited his son while he served in Iraq in 2009

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Biden said his son was "the finest man any of us have ever known"

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Mr Biden took his oath of office as senator in 1973 by Beau's hospital bed

"Beau embodied my father's saying that a parent knows success when his child turns out better than he did," he said, adding: "We know that Beau's spirit will live on in all of us."

"Beau Biden was, quite simply, the finest man any of us have ever known," the statement ended.